Morcilla rellena

A blood sausage is a sausage filled with blood that is cooked or dried and mixed with a filler until it is thick enough to solidify when cooled. Most commonly, the blood of pigs, sheep, lamb, cow, chicken, or goose is used. In Europe and the Americas, typical fillers include meat, fat, suet, bread, cornmeal, onion, chestnuts, barley, oatmeal, and buckwheat. On the Iberian Peninsula and in Latin America and Asia, fillers are often made with rice. Sweet variants with sugar, honey, orange peel, and spices are also regional specialties.

Source: Wikipedia